Transparent electrodes are required in the fields of solar cells, transparent thermal wires and flat panel display devices including devices such as liquid crystal display devices, plasma display devices, field emission display devices, and organic electron light emitting display devices. Tin oxide SnO2 and zinc oxide ZnO are used to form the transparent electrodes. However, a representative material used to form the transparent electrodes is indium tin oxide (ITO). ITO is a widely used material for forming transparent electrodes since ITO has high optical transmittance in a visible light region and has relatively high electrical conductivity.
An ITO thin film can be formed using a spray chemical vapor deposition (CVD) method, a sol-gel method, a thermal evaporation method, an e-beam evaporation method, a direct current electroplating method, a high-frequency sputtering method, or a reactive DC sputtering method. The ITO thin film is used as a transparent electrode by patterning it to a predetermined shape.
FIGS. 1 through 3 are cross-sectional views for explaining a conventional method of patterning an ITO thin film using an etching process.
Referring to FIG. 1, as described above, an ITO thin film 12 can be formed on a substrate 10 using various methods. A photoresist film 14 is coated on the ITO thin film 12. A photomask 20 is contacted on the photoresist film 14. A fine pattern 18 of a desired shape is formed on a mask substrate 16 of the photomask 20. While the photomask 20 contacts the photoresist film 14, ultraviolet rays 22 are selectively exposed onto the photoresist film 14 using an exposure apparatus (not shown).
Referring to FIGS. 2 and 3, a photoresist pattern 14a of a desired shape is formed by developing the exposed photoresist film 14. An ITO pattern 12a is formed by patterning an ITO thin film 12 using a wet etching method, a dry etching method, or etching by radiating a laser using the photoresist pattern 14a as a mask. Next, the patterning of the ITO thin film 12 is completed by removing the photoresist pattern 14a. 
However, the conventional method of patterning an ITO thin film uses a wet etching method, a dry etching method, or etching by radiating a laser as an etching method. The wet etching method has advantages in that the etching process is simple and it has a high through-put. However, the wet process has drawbacks in that the exfoliation of photoresist pattern occurs during an etching process due to a weak bonding force between the photoresist pattern and the ITO thin film, and the exfoliated photoresist pattern can contaminate an etching bath. Furthermore, the wet etching method is not appropriate for forming a nano scale fine pattern due to isotropical etching characteristics of the wet etching.
The dry etching method can form a fine pattern of 5 μm or less, however, has a low through-put, and has a problem in which re-depositing of the photoresist occurs during the etching process. The etching method that uses a laser can form a fine pattern of approximately 1 μm, however, this method is only effective for forming an ITO pattern of a simple matrix stripe shape.
FIGS. 4 through 6 are cross-sectional views illustrating a conventional method of patterning an ITO thin film using a lift-off process.
Referring to FIG. 4, a photoresist film 32 is coated on a substrate 30. A photomask 38 is contacted on the photoresist film 32. A fine pattern 36 of a desired shape is formed on a mask substrate 34 of the photomask 38. While the photomask 38 contacts the photoresist film 32, ultraviolet rays 40 are selectively exposed onto the photoresist film 32 using an exposure apparatus (not shown).
Referring to FIGS. 5 and 6, a photoresist pattern 32a of a desired shape is formed by developing the exposed photoresist film 32. An ITO thin film 42 is formed on the entire surface of the substrate 30 on which the photoresist pattern 32a is formed using one of methods described above. Next, an ITO pattern 42a is formed by removing the photoresist pattern 32a and the ITO thin film 42 using a lift-off method.